The present invention relates to a process for the isolation of a polyarylene ester from a solution of a polyarylene ester in an organic solvent. More particularly, it relates to a process for the isolation of a particulate, uniform polyarylene ester solid having a high bulk density and good thermal stability and hydrolytic stability from a solution of a polyarylene ester in an organic solvent, said polyarylene ester being obtained by polycondensing dihydric phenol compounds with aromatic dicarboxylic acids or aromatic dicarboxylic acid derivatives.
Polyarylene esters obtained from aromatic dicarboxylic acids or derivatives thereof, such as dicarboxylic acid dichloride and dihydric phenol compounds, are polymers which are good in thermal stability as well as in fire retardency and excellent in mechanical and other various properties. As a process for the preparation of the said polymers are known interfacial polycondensation, solution polycondensation and melt polycondensation processes.
In particular, the interfacial polycondensation process gives a polymer with high degrees of polymerization at low temperature and has thus far been generally regarded as advantageous in terms of a commercial process. The conventional interfacial polycondensation technique for the production of polyarylene ester utilizes the interface between water and a water-insoluble organic solvent, such as dichloromethane, dichloroethane, xylene or toluene, to perform the polycondensation reaction. It is dichloromethane or dichloroethane in which the polymer formed dissolves, in particular that is well used. In this case, polyarylene ester is obtained as a solution in a water-insoluble organic solvent, such as dichloromethane.
The desired polymer is generally isolated from the reaction mixture obtained by this process following the procedure involving, first, separating the reaction mixture into a polymer solution layer and an aqueous layer, subjecting the polymer solution to a purification treatment to remove impurities present (such as a sodium salt of unreacted dihydric phenol compound and NaCl formed as a by-product by the reaction) insofar as possible, and then separating the polymer from the purified polymer solution. The purification treatment of the polymer solution is usually carried out by repeating a procedure of washing the polymer solution with a great deal of an alkaline or acidic aqueous solution or water and then separating the organic layer from the aqueous layer. The polymer from the purified polymer solution is usually isolated by concentrating the polymer solution to gel the polymer, or by contacting the polymer solution with a great deal of a poor solvent for the polymer, such as acetone or methanol, to precipitate and then filter the polymer.
The said process of subjecting the polymer solution to purification treatment in advance and then separating the polymer from the polymer solution entails many such drawbacks as to be complicated in a cleansing operation, an operation for separation into the organic layer and the aqueous layer and an operation for solidification and isolation of the polymer, or to be inefficient in recovery of a poor solvent, such as methanol and acetone and of a reaction solvent, such as dichloromethane and dichloroethane.
Proposals have been made for the process designed to overcome these drawbacks. Mention can be made, for instance, of a process which comprises concentrating suitably a solution of a polymer obtained by the interfacial polycondensation process in dichloromethane, followed by addition to the concentrated solution of predetermined amount of a poor solvent for the polymer whereby the polymer can be isolated as finely divided solids (Japanese Laid-Open Patent Application (KOKAI) No. 49-78794) or of a process which comprises diluting a solution of a polymer in dichloromethane by addition of a poor solvent for the polymer until the polymer solution reaches the cloud point, and aging the dilute solution, followed by further addition of the poor solvent whereby the polymer can be isolated as finely divided solids (Japanese Laid-Open Patent Application (KOKAI) No. 14598). True, these processes are considered practical as compared with prior art processes, but it is still required to use a comparatively great deal of a poor solvent, and in many cases, it takes a considerable time before it is finely divided. Often, the polymer isolated is not always good in thermal stability, as well as in hydrolytic stability. Thus, these processes still entail a variety of defects.
In some embodiments of the said improved processes, alochols are used as a poor solvent to be added to the solution of polyarylene ester in an organic solvent. The instant inventors learned that when alcohols were used in 0.1-1.0-fold amounts, by weight ratio, based on the solution of the polymer in the organic solvent in such an embodiment, the polymer could be obtained as rice cake-like coagulated solids, which could be no more finely divided as particulate solids in the solution.
The primary purpose of the present invention is to provide a practical process of isolating polyarylene ester as particulate solids from a solution of polyarylene ester in an organic solvent. Another purpose of the present invention is to obtain polyarylene esters having good thermal stability and hydrolytic stability in comparison with polyarylene esters obtained by conventionally known isolation methods.